Nylon tire cord



United States Patent Patented June 30, 1970 US. Cl. 156--110 14 ClaimsABSTRACT OF THE DISCLOSURE Nylon reinforced vehicle tires have minimumflatspotting when the reinforcing cords that are embedded into therubber plies of the tires have diffused throughout the yarns which makeup the cords an organic hydroxylated plasticizer in an amount sufficientto decrease the cord modulus prior to hot stretch processing by at leastpercent. After the cords have been subjected to hot stretch processing,a definite increase is observed in their modulus.

This is a division of application Ser. No. 426,661, filed Jan. 19, 1965,now abandoned.

This invention relates to textile cords employed as reinforcement forrubber vehicle tires. More particularly, this invention relates to nylontire cord which is particularly resistant to flatspotting.

The use of nylon as a reinforcing fiber for rubber vehicle tires is wellknown to the art. Other fibers such as cotton, rayon, etc. have alsobeen used in this capacity but nylon is preferred due to its superiorqualities such as higher tenacity, improved fatigue resistance, andsuperior wearing quality. On the other hand, nylon possesses a seriousdrawback when used to reinforce vehicle tires in that such tires have asignificant tendency to flatspot. Flatspotting is a phenomenon whichoccurs when an inflated tire is operated for a period of time on avehicle and then is allowed to stand at rest. The area of the tire whichis in contact with the surface on which it rests becomes flat, thuscreating a flattened portion on the circular tire which, on standing,sets in place. This phenomenon is not completely understood but isthought tobe associated with the complex forces of compression andtension which are different at the area of the tire which is resting onthe surface than in the other portions of the tire, and to theelongation-contraction properties of the nylon cord. When a vehicle isstarted, this flatspot causes considerable vibration and bumping eachtime the tire rotates. Of course, after the tire is again operated for aprolonged period it becomes warm and thus the flatspot disappears. Theperiod of time and the amount of mileage necessary to eliminate theflatspot is one method of measuring the flatspot and is referred to asrunout. Another method of measuring the amount of flatspot is the depthof the flatspot.

It is an object of this invention to provide a nylon tire cord which isparticularly resistant to flatspotting.

It is a further object of this invention to provide a process forproducing a nylon tire cord which is particularly resistant toflatspotting.

It is a still further object of this invention to provide a vehicle tirereinforced with nylon cord which exhibits minimum flatspotting.

These and other objects will become apparent from the description givenhereinafter.

The term nylon as used herein is intended to denote fibers produced fromsynthetic linear polycarbonamides which contain recurring carbonamidelinkages as an integral part of the polymer chain. These polyamides arewell known in the art and are generally referred to therein as nylons.Since these polyamides are well known to the art, a lengthy discussionof their exact nature would serve no useful purpose herein. However, itmay be pointed out that these polyamides are produced by thepolymerization reaction between a dicarboxylic acid and a diamine, or bythe interpolymerization of an amino acid. Typical nylons suitable foruse in accordance with the present invention are polyhexamethyleneadipamide (nylon 66), polyhexamethylene sebacamide (nylon 610),polyhexamethylene dodecanediamide (nylon 612), polycaproamide (nylon 6),and the like. The preferred nylons for use as reinforcing fibers forrubber vehicle tires in accordance with the present invention arepolyhexamethylene adipamide (nylon 66) and polycaproamide (nylon 6). Thenylons used as reinforcing fibers for the articles of the presentinvention may be either homopolyamides or copolyamides or mixtures ofthe same.

The term rubber vehicle tires as used herein is meant to include vehicletires made from natural rubber and synthetic rubber such as butyl,chloroprene, thiokols, buna, and styrene-butadiene rubbers, as well asmixtures of such synthetic rubbers and mixtures of synthetic and naturalrubbers. The rubber vehicle tires referred to herein are meant toinclude those tires in which are employed conventional additives such asvulcanization agents, antioxidants, extenders, carbon black and thelike.

The term cord modulus as used herein refers to the modulus as determinedby ASTM Method D885-64T, Section 36. While the modulus may be determinedat any given temperature, for purposes of uniformity, the cord modulusvalues referred to herein were all determined at 25 C.

A recent significant advance in the area of nonflatspot ting nylon tireshas been the discovery that tires reinforced with nylon tire cords whichhave a moisture content greater than 3 percent result in a significantreduction in the flatspotting severity of the tire. However, due toadhesion and vulcanization problems resulting from the presence ofwater, it has been found necessary that the water be introduced into thenylon cords after the fabrication of the tire. This need for posttreating has the obvious disadvantage of adding an additional processstep to an already complex process for fabricating nylon reinforcedvehicle tires.

We have now found quite unexpectedly that nylon reinforced tires showminimum flatspotting results when the reinforcing cords are conventionalpolyamide (nylon) tire cords which have a total denier above 1000 andhave diffused therein, substantially throughout the individual yarnswhich make up the tire cord, an organic, hydroxylated plasticizer in anonmolecular, intersticial relationship to the cord molecules, and in anamount sufficient to decrease the cord modulus at 25 C. of the nyloncord by a value of at least 10 percent. This discovery is surprisinginasmuch as prior to this time, it has been generally thought thatplasticization of nylon tire cord would adversely affect thefiatspotting, that is, the flatspot severity of the tires produced fromplasticized nylon cords would increase. We have found however, thatwhile the nylon tire cord of the present invention which is plasticizeddoes show the effects of plasticization prior to introduction into thetire, for example, the decrease in modulus, these plasticization effectsdo not exist, at least not in the theorized manner, on the tire asfinally fabricated from these cords.

A normal tire cord which is to be used to reinforce rubber vehicle tiresgoes through certain processing steps prior to the fabrication of thetire. These processing steps are conventional and well known in the artof tire making. Thus, conventionally, a cord which is about to be usedin the tire is first dipped in an adhesive solution, for example, aresorcinol-formaldehyde rubber latex, and thereafter dried by passingthrough two drying zones. The first of these zones is generallymaintained between about 300 F. and about 350 F. and, while passingthrough this zone, sufficient tension is applied to the cord to stretchit about 3 percent. The dwell time in this first zone is about "60seconds. The cord upon emerging from this first zone is passed into asecond zone and stretched about 9 percent while heated to a temperatureof between about 400 and 500 F. with a dwell time of from 20 to 60seconds. The nylon tire cords of the present invention, due to theirnovel characteristics, require a slight modification in thisconventional process. When a nylon cord of the present invention ispassed through the adhesive dip prior to any drying step, it is foundthat it does not pick up enough adhesive to function properly in thetire. Thus, in accordance with the process for producing nonfiatspottingvehicle tires with the nylon tire cords of the present invention, thetire cord which already contains a plasticizer diffused therein ispassed through the first drying zone which is maintained at betweenabout 300 F. and 350 F., while sufficient tension is applied to the cordto allow about a 3-percent stretch and for a dwell time of about 60seconds, thereafter the cord is dipped in an adhesive solution and thenpassed through the second drying zone heated to between about 400 F. andabout 500 F. for a dwell time of about 20 to 60 seconds and withsuflicient tension applied to the cord to allow a stretch of about 9percent. When the nylon tire cords of the present invention areprocessed in this manner, it is found that when they emerge from thishot stretching operation, the effects of plasticization are no longerevident inasmuch as the 25 C. cord modulus of the cord prior tointroduction through this hot stretch process was less, by at least 10percent than the 25 C. cord modulus of normal nylon whereas the emergingcord shows a definite increase in modulus. As is obvious to anyoneskilled in the art, analysis of the cords at this point is extremelydifficult. Therefore, just what happens to these cords is not known atthis time. While not wishing to be bound to any specific theory ofoperation, it is postulated that some chemical reaction occurs eitherbetween the plasticizer additive and the adhesive dip or between theplasticizer additive and the nylon polymer or between the plasticizeradditives themselves or between any combination of these. In any event,it is known that plasticized cords according to the present invention,when passed through this hot stretching operation and then used toreinforce rubber vehicle tires show greatly superior results in regardto the flatspotting tendencies of the tires.

It has also been observed that the boiling water shrinkage of the nylontire cords of the present invention prior to the heat stretchingtreatment is increased substantially, in some cases by as much as 0percent, and in all cases at least as much as about percent, over theboiling water shrinkage of untreated nylon cords. This means that thecords of the present invention shrink to a greater extent when treatedwith boiling water than do conventional, or untreated nylon cords. Thisagain is surprising inasmuch as prior to this time it has been thoughtthat cords which exhibited high boiling water shrinkage performed poorlywhen used as reinforcement for vehicle tires inasmuch as the flatspotseverity increased. However, the cords of the present invention,although exhibiting an increased boiling water shrinkage prior to theheat stretching treatment show excellent flatspotting properties whenthey are fabricated into a tire after they are heat stretched.

The term organic hydroxylated plasticizer as used herein is meant toinclude organic compounds which contain at least one hydroxy group andact as a plasticizer for nylons, that is, act in such a way that thecord modulus of the nylon is decreased. Normally these organicplasticizers contain less than ten carbon atoms and preferably less thanseven. They are a liquid at ambient temperatures, that is 20 to 50 C.,and have a boiling point above about 150 C. Typical suitableplasticizers which may be used in accordance with the present inventionare ethylene glycol, diethylene glycol, triethylene glycol, benzylalcohol, glycerol, and the like. The amount of plasticizer that must bediffused throughout the nylon cord in order to render themnonfiatspotting when fabricated into a tire is critical only to theextent that there must be substantial diffusion of the plasticizer intothe cord so that the plasticizer exists in a non-molecular, intersticialrelationship with the polyamide molecules of the nylon, and must havethe effect on the nylon cord of decreasing the 25 C. cord modulus by atleast 10 percent. The exact amount of plasticizer that must be presentvaries depending on the plasticizer used, the particular nylon inquestion, and the amount of reduction in flatspot that is necessary.Having these factors in mind, it may generally be said that the amountof plasticizer added to the nylon is normally within the range of 0.5 to15 percent of plasticizer based on the weight of the nylon, with 2 to 3percent being preferred.

The manner in Which the plasticizer is introduced into the nylon tirecord is also not critical except to the extent that the plasticizer mustbe introduced after extrusion of the yarns and before the hot stretchingoperation. Thus, the plasticizer may be introduced into the individualyarns prior to the production of the cord or the plasticizer may beadded to the cord itself providing that there is substantial diffusionof the plasticizer into the individual yarns which make up the cord. Theplasticizer may conveniently be introduced into the cord or the yarnswhich make up the cord by dipping either the cord or the yarns into anaqueous solution of plasticizer which may range in concentration from 10percent plasticizer to percent plasticizer.

In order to more fully and clearly illustrate the present invention, thefollowing specific examples are presented. It is intended that theexamples be considered as illustrative only and not limitative.

EXAMPLE I A three-ply, ten by ten twist cord of nylon 66(polyhexamethylene adipamide) having a total denier of 2850 was passedthrough a container containing 100 percent ethylene glycol at a rate of15.6 yards a minute and wound on a takeup bobbin. The cord modulus at 25C. was measured at 11 grams per denier. After storing for two weeks,this cord was then processed with a Litzler hot stretching machine priorto dipping. In the Litzler machine, the first zone was heated to 325 F.with sufficient tension applied to the cord to allow a 3-percent stretchand a dwell time of 60 seconds. The cord was then passed through aconventional resorcinol-formaldehydelatex dip and then through a secondzone heated to 450 F. with sufficient tension applied to allow a9-percent stretch and a dwell time of 30 seconds. These cords wereimmediately embedded into rubber sheets which were made into plies andthe plies were built into a tire after an overnight storage. The tirewas mounted on a rim and loaded to 1175 pounds against a 67-inchdiameter driving wheel. The tire was then run for 15 minutes at 30 milesper hour after which it was held at rest under load for 4 hours. Thistest is hereinafter termed a 15/ 30/4 test. This tire was tested forflatspot and found to have a flatspot depth of 118 mils. The tire wasthen tested under the same load by running for 30 minutes at 60 milesper hour after which it was allowed to rest for 2 hours (a 30/ 60/ 2test). The flatspot level of this test was 112 mils.

In the following examples, 3-ply, ten by ten twist nylon 66 tire cordshaving a total denier of 2850 were processed in a manner identical tothat described in Example I with the exception that the plasticizeremployed and the concentration thereof is as indicated:

Cord modulus Flatspot at 25 C.

A nylon 66 tire yarn having a denier of 840 was run through a containerof 100 percent ethylene glycol at a rate of 26 yards per minute andwound on take up bobbins. After six days storage, this yarn was twistedinto a ten' by ten twist 3-ply cord which had a cord modulus of 11 g./d.The cord was then processed through the Litzler machine and fabricatedinto a tire by the procedure as described in Example I. The tirescontaining the cord produced from the ethylene glycol treated yarn had aflatspot level of 120 rnils for 15/ 30/ 4 while a control tire, that is,a tire fabricated with untreated cord had an average flatspot value of150 mils for this test.

It can thus be seen that nylon tire cord treated with the organichydroxylated plasticizers in accordance with the present inventionresult in a significant reduction in flatspotting when these cords areused to reinforce vehicle tires. It can also be seen from the aboveexamples that the plasticizers need only be added at any point prior tothe hot stretching operation which is conventional for treating cordsjust prior to their introduction into a tire.

It will be apparent that many widely different embodi- 3 which make upthe cord, an organic, hydroxylated plasticizer in a nonmolecular,intersticial relationship to the cord molecules, and in an amountsuificient to decrease the cord modulus of the cord at 25 C. by at least10 percent, (2) subjecting said cord to sufiicient tension to stretchsaid cord at least 3 percent while heating said cord to a temperatureabove 300 F., (3) thereafter embedding said cord into rubber plies and(4) fabricating a rubber vehicle tire from said plies.

2. The rubber vehicle tire produced by the method of claim 1. r

3. The method of claim 1 wherein the nylon tire cord is nylon 66.

4. The tire produced by the method of claim 3.

5. The method of claim 3 wherein the organic hydroxylated plasticizer isethylene glycol.

6. The tire produced by the method of claim 5.

7. The method of claim 3 wherein the organic hydroxylated plasticizer isdiethylene glycol.

8. The tire produced by the method of claim 7.

9. The method of claim 3 wherein the organic hydroxylated plasticizer istriethylene glycol.

10. The tire produced by the method of claim 9.

11. The method of claim 3 wherein the organic hydroxylated plasticizeris glycerol.

12. The tire produced by the method of claim 11.

13. The method of claim 3 wherein the organic hydroxylated plasticizeris benzyl alcohol.

14. The tire produced by the method of claim 13.

References Cited UNITED STATES PATENTS 4/1968 Robertson. 6/1968 Brignac.

OTHER REFERENCES Bayerlein et al.: Chem. Abstracts, vol. 60, p. 16088(1964).

LELAND A. SEBASTIAN, Primary Examiner

